1. Field of the Invention
The present invention relates to a plasma display apparatus and method for driving the same.
2. Background of the Related Art
Generally, a plasma display panel (hereinafter, referred to as a “PDP”) is adapted to display an image including characters or graphics by light-emitting phosphors with ultraviolet of 147 nm generating during discharging of an inert mixed gas such as He+Xe or Ne+Xe.
FIG. 1 is a perspective view illustrating the construction of a conventional three-electrode AC surface discharge type PDP having a discharge cell structure arranged in the matrix form.
Referring to FIG. 1, the three-electrode AC surface discharge type PDP 100 includes a scan electrode 11a and a sustain electrode 12a formed on a bottom surface of an upper substrate 10, and an address electrode 22 formed on a top surface of a lower substrate 20. The scan electrode 11a and the sustain electrode 12a are formed using a transparent electrode, for example, indium-tin-oxide (ITO). Metal bus electrodes 11b, 12b for reducing resistance are formed in the scan electrode 11a and the sustain electrode 12a, respectively. On the bottom surface of the upper substrate 10 in which the scan electrodes 11a and the sustain electrode 12a are formed are laminated an upper dielectric layer 13a and a protective layer 14. The upper dielectric layer 13a is accumulated with a wall charge generated during plasma discharging. The protective layer 14 is adapted to prevent damages of the upper dielectric layer 13a due to sputtering caused during the plasma discharging, and improve the efficiency of secondary electron emission. As the protective layer 14, magnesium oxide (MgO) is generally used.
Meanwhile, a lower dielectric layer 13b and barrier ribs 21 are formed on the lower substrate 20 in which the address electrode 22 is formed. A phosphor layer 23 is coated on the surfaces of both the lower dielectric layer 23b and the barrier ribs 21. The address electrode 22 is formed in a direction where it intersects the scan electrode 11a and the sustain electrode 12a. The barrier ribs 21 are formed in parallel to the address electrode 22, and serves to prevent leakage of an ultraviolet and a visible light generated by discharging to neighboring discharge cells. A phosphor layer 23 is excited with an ultraviolet generated during plasma discharging to generate any one of red (R), green (G) and blue (B) visible light. An inert mixed gas such as He+Xe or Ne+Xe is injected into discharge spaces of discharge cells, which are defined by the barrier ribs 21 between the upper substrate 10 and the lower substrate 20. A method for driving the conventional PDP constructed above will now be described with reference to FIG. 2.
FIG. 2 shows a driving waveform for explaining a method for driving the conventional PDP. Referring to FIG. 2, the conventional PDP is driven with be being divided into a reset period for initializing the entire screen, an address period for selecting a cell, and a sustain period for sustaining discharge of a selected cell.
First, the reset period is driven with it being divided into a set-up period SU and a set-down period SD. In the set-up period SU, a ramp-up waveform Ramp-up is applied to all scan electrodes Y at the same time. Discharging is generated within cells of the entire screen by means of the ramp-up waveform. This set-up discharge causes wall charges of the positive polarity to be accumulated on the address electrode X and the sustain electrode Z, and wall charges of the negative polarity to be accumulated on the scan electrode Y. In the set-down period SD, after the ramp-up waveform is supplied, a ramp-down waveform Ramp-down, which drops from a positive voltage lower than a peak voltage of the ramp-up waveform to a ground voltage GND or a predetermined negative voltage level, causes a weak erase discharge to occur within the cells, thereby erasing some of wall charges that are excessively formed. This set-down discharge causes wall charges of the extent that an address discharge can be generated stably to uniformly remain within the cells.
In the address period, while a negative scan pulse SCAN is sequentially applied to the scan electrodes Y, a positive data pulse data is applied to the address electrodes X in synchronization with the scan pulse. As a voltage difference between the scan pulse and the data pulse and a wall voltage formed in the reset period are added, an address discharge is generated within cells to which the data pulse is applied. The address discharge causes wall charges of the extent, which can generate discharging when a sustain voltage is applied, to be formed within a selected cell. To the sustain electrode Z is applied a positive DC voltage Zdc so that erroneous discharge with the scan electrodes Y is not generated through reduction of a voltage difference with the scan electrodes Y during the set-down period and the address period.
In the sustain period, a sustain pulse SUS is alternately applied to the scan electrodes Y and the sustain electrodes Z. A sustain discharge, i.e., a display discharge is generated between the scan electrodes Y and the sustain electrodes Z of a cell selected by the address discharge whenever the sustain pulse is applied as the wall voltage within the cell and the sustain pulse are added. Further, after the sustain discharge is completed, a ramp waveform Ramp-ers having a narrow pulse width and a low voltage level is supplied to the sustain electrodes Z, thereby erasing wall charges remaining within cells of the entire screen.
On the other hand, the operation of the driving apparatus of the PDP in the address period and the sustain period will be below described in more detail with reference to FIGS. 3 and 4.
FIG. 3 is a circuit diagram for explaining a driving apparatus that operates in the address period and the sustain period of the conventional PDP. FIG. 4 shows waveforms of a scan pulse and a sustain pulse in the prior art.
As shown in FIGS. 3 and 4, if a Y1 electrode is selected in the address period, two switching elements 211-1,213-1 included in a scan driver 210-1 corresponding to the Y1 electrode, A switching element 220 for scan and a switching element 230 for bias are turned on. At the same time, switching elements 211-2 to 211-n located at the top, among two switching elements included in scan drivers 210-2 to 210-n corresponding to remaining Y electrodes Y2 to Yn that are not selected, are turned on, and switching elements 213-2 to 213-n located at the bottom are turned off.
Accordingly, a scan pulse voltage applied to selected Y electrodes varies between a bias voltage—Vbias and a scan voltage—Vyscan, and the potential of Y electrodes that are not selected becomes a bias voltage—Vbias.
Furthermore, in order for a sustain pulse to be applied to the Y electrodes in the sustain period, the switching elements 211-1 to 211-n, 213-1 to 213-n included in the scan drivers 210-1 to 210-n, the switching element 220 for scan and the switching element 230 for bias are all turned off, and a switching element 240 for sustain and a switching element 260 for ground are turned on. Accordingly, a voltage Vsy is applied to the Y electrodes through a diode located on a lower side of the scan drivers 210-1 to 210-n.
Furthermore, in order for a sustain pulse to be applied to the Z electrodes in the sustain period, the switching element 250 for sustain and the switching element 230 for bias are turned on, and switching elements included in the scan drivers 210-1 to 210-n, the switching element 220 for scan and the switching element 240 for sustain are turned off. As such, a voltage Vsz is applied to the Z electrodes.
In case of the prior art, since the voltage level of the sustain pulse applied to the Y electrodes and the Z electrodes in the sustain period varies from OV to Vsy or Vsz, the X electrodes being a data electrode are always charged with positive ions. As such, in the process where the X electrodes are charged with positive ions, the positive ions collide against phosphors, which shortens the lifespan of phosphors. Moreover, as particles generated by collision of the positive ions are adhered on the surface, they degrade brightness. This is because the shock of a case where positive ions collide against phosphors is over several thousands of times stronger than a case where negative ions collide against phosphors since the mass of the positive ions is very higher than that of the negative ions.
Further, the voltage level of the Z electrodes in the address period is a ground level, and the voltage level of the Y electrode is a bias voltage—Vbias. As a bias voltage as much as a predetermined voltage is applied from the Z electrodes to the Y electrodes, a voltage difference occurs. This voltage difference always serves as leakage to increase power consumption, and also has a bad influence on the operation of a driving apparatus.
In addition, since the bias voltage—Vbias in the address period and the bias voltage being the ground level in the sustain period are different from each other, a circuit of the driving apparatus is complicated, and is influenced by noise.